Traditional telecommunications service networks separate the systems used for signaling and user data. This separation is intended to create redundancy and fault tolerance to data throughput constraints. However, with the growth of Long Term Evolution (LTE) networks, there have been many discussions and papers written about signaling storms. Signaling storms, as used herein, are events during which heavy traffic significantly reduces the signaling capacity of a network; they differ from ordinary network congestion in that it is limited signaling capacity, not limited data capacity, that is the constraint.
Why is signaling load growing to such an extent? One reason is the flatter architecture of LTE networks as compared with 3G networks. In 3G networks, the Radio Network Controller (RNC) resides between the base station and core network elements, effectively shielding the core network from the mass of signaling generated by the radio access network for mobility management. Because LTE uses a flat architecture, it eliminates the RNC. The core network is connected directly to the LTE base stations, in LTE, which means that it has to handle all signaling traffic. All networks having a flat architecture are, to some extent, vulnerable to signaling overload in this way.
A corollary is that the failure of one element in the core network can have consequences for a large number of base stations and UEs. For example, a single home subscriber server (HSS) may provide identity services for all subscribers on the network, and may provide these services to hundreds of eNodeBs. As another example, a single mobility management entity (MME) can provide mobility management also for hundreds of eNodeBs. The failure of an MME can cause hundreds of mobile devices to become unable to access the network.
If a single HSS or MME fails, the consequences may include a signaling storm, as all eNodeBs and/or UEs connected to that HSS or MME may attempt to reconnect to another core network node at the same time, causing a spike in traffic similar to a denial-of-service attack.